Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $22.66   6.858%   $24.214   $24.21   $24.20   $24.20  
  Purchase #2 $189.44   10.271%   $208.8974   $208.90   $208.90   $208.90  
  Purchase #3 $117.28   6.576%   $124.9923   $124.99   $125.00   $125.00  
  Purchase #4 $162.50   11.783%   $181.6474   $181.65   $181.65   $181.60  
  Purchase #5 $207.90   13.316%   $235.584   $235.58   $235.60   $235.60  
  Purchase #6 $155.87   12.598%   $175.5065   $175.51   $175.50   $175.50  
  Purchase #7 $248.83   8.117%   $269.0275   $269.03   $269.05   $269.00  
  7 purchase totals = $1,104.48       $1,219.8691   $1,219.87   $1,219.90   $1,219.80